Method for the production of material for printed circuits

ABSTRACT

A method for the production of a material for printed circuits is disclosed. A temporary base is coated by electroplating with a thin, unbroken and unpatterned metallic layer having a thickness less than 17μm and the free surface of said metallic layer is bonded to a final insulating base. The temporary base is thereafter removed and the desired wiring pattern is produced by a process comprising etching of the metal layer. A material for use in production of printed circuits is also disclosed comprising a temporary base which is coated by electroplating with a thin, unbroken and unpatterned metal layer having a thickness less than 17μm. Said material can comprise a final, insulating base bonded to the free surface of the thin metal layer.

This is a continuation of application Ser. No. 283,955, filed Aug. 28,1972, now abandoned.

The present invention relates to a method for producing material forprinted circuits, said material comprising a thin layer of metal on aninsulation-carrier or base.

Printed circuits are used to a large extent in the electronics industry.They are usually produced with a copperclad plastic laminate as startingmaterial. A copy of the desired wiring pattern is transferred to thecopper layer by printing or by a photochemical method. The applied copy,the so-called etch resist acts as a protection during a subsequentelimination by etching of superfluous copper. Thereafter electroniccomponents are mounted to the laminate with the circuit thus obtained.The copper conductors of the circuit constitute the electricalconnections and the laminate provides the required mechanical support.This technique provides good possibilities of space and weight savingbuild-up of the electronic unit. The method affords high reliability andrational production.

The most common bases are paper-reinforced phenolic laminates which areused for comparatively simple circuits, and glass cloth reinforced epoxyresin laminates which are used where the technical requirements arehigh. Use is also made of fibre reinforced plastic laminates of othertypes. Base materials of the type plastic films and plastic coated metalplate are also used to a certain extent. For producing the coppercoating or layer it is common to use copper foils or sheets which areplaced on a base-forming fibre material impregnated with partially curedor hardened plastic (so called prepreg) whereupon the composite materialis moulded at high pressure and increased temperature. The final curingof the plastic is thereafter effected whereby the fibre material isconverted into a sheet bonded to the copper foil. The copper foil hasusually a thickness of 35 μm, but also thicker and thinner foils can beused. According to another known method of the copper foil is glued to aplastic film by means of heat and pressure.

Owing to the rapid development in the electronics field the demand forprinted circuits with good dimensional precision, especially incircuitry with small line width and small distances between conductors,is increasing. Already at present printed circuits with a line width of0.2 mm are required in many cases. Even smaller dimensions have beenused and the need thereof is supposed to increase in the future. Thisdevelopment has led to a demand for laminates with thinner copperlayers. Lately laminates with 17 μm thick copper foils have come intouse to an increasing extent. By using thinner copper foils advantagesare gained, i.a. a decrease of so-called "undercut". By undercut ismeant the elimination of copper under the etch resist caused by theetching solution which while dissolving the unprotected portions of thecopper layer also eats into the copper covered by the etch resist. Theundercut is a difficult problem causing unacceptably low dimensionalaccuracy especially in circuits with fine-line conductors. The effect ofthe undercut at varying thickness of the copper layer shall be explainedin more detail in the following description.

By means of a suitable technique it is possible to obtain a high degreeof precision in the application of the etch resist proper. However,owing to the undercut, difficulties arise in maintaining the gooddimensional accuracy as to, for instance, the line width which thetechnique involving masking by means of an etch resist makes possibleper se.

For some applications, very exactly defined distances between conductorsare required, even for ordinary-dimension circuits. This is particularlytrue in applications, where electrical influence between conductors mustbe considered, i.a. in electronic systems which are to operate at highfrequencies.

Thin copper-layer clad laminates can be used with advantage also forthis purpose.

There are other advantages with thinner copper layers. Thus, the etchingtime is considerably reduced and the amount of etching solution consumedis also reduced. The amount of copper required for obtaining the copperlayer is likewise reduced. For these reasons thin copper layers can befavorable also if the requirements as to the dimensional accuracy arenot very high.

If an increased thickness of the copper conductors is desirable thethickness can be increased by chemically or electolytically depositingcopper according to known techniques. By this procedure copper isdeposited only on the portions of the copper layer constituting theconductors of the final printed circuit which portion usually is theminor portion of the total surface of the printed circuit. By suitabletechniques the increase of the thickness of the copper layers can beeffected with good dimensional accuracy and in the case of insulationbases which are provided at both sides thereof with a conductor patternof copper the increase of the copper thickness can suitably be carriedout in connection with a so-called through-holes plating which is amethod often used for providing electrical connections between theprinted circuits on each sides of the base and for providing holes forthe mounting of electrical components. Thus, no extra process step isrequired to increase the thickness of the conductors. The method alsogives the advantage that the main portion of the conductors of thecircuit and the copper layer in the holes will consist of homogenous andsimultaneously deposited metal which is favorable from the point of viewof reliability.

From the above discussion the advantages gained by using bases withthinner metal layers than what is usual at present in the manufacture ofprinted circuits clearly appear. In a common method for the productionof metal coated, insulating bases for printed circuits an unbroken orcontinuous, non-patterned metal foil or sheet is used as a startingmaterial which foil is bonded to the base by moulding at increasedtemperature or in other manner. The most commonly used metal foil is acopper foil produced electrolytically. Such a copper foil has a highdegree of purity. However, considerable problems occur if an insulatingbase with a copper foil having a thickness less than 17 μm shall beproduced according to this method, since there are great difficulties inconnection with the practical handling of such thin copper foils.Another considerable disadvantage of this known method in the case ofvery thin copper foils produced electrolytically is due to the fact thatthe copper foil has often cavities and through-going holes, so calledmicropores, the latter being, for reasons easily realized, moredifficult to avoid with decreased thickness of the foil. During themoulding of the laminate still uncured resin material can penetratethrough the pores and accumulate on the free surface of the foil whereit can give raise to great difficulties i.a. during the subsequentetching of the copper foil when the resin on the surface act as anunwanted etch-resist.

Another method has been suggested according to which a thin copper layeris deposited on an insulating base by direct plating on the base. Suchplating must be effected at least partly by other method than byelectroplating since the carrier is of an insulating material. Anapplied method is chemical plating which, however, is comparativelyexpensive and complicated. Thus, for instance, the surface of thelaminate must often be pretreated for assuring good bonding of thedeposited copper. This pretreatment can give rise to deep cavities inthe base which cavities will be filled by copper at the platingprocedure. This necessitates relativvely long etching times for assuringthat all copper is removed from the etched portions of the laminate. Theprolonged etching time increases the production costs and will also leadto an increased undercut even in the case of laminates with thinchemically deposited copper layers.

For completing the picture of the prior art in the manufacture ofmaterials for printed circuits a method shall be mentioned which isdescribed in, for instance, the U.S. Pat. No. 2,692,190. According tothis patent a final wiring pattern of copper is applied to or formed ona temporary base whereupon this base with the pattern facing a final,insulating base, and with the resin material of the base still uncuredis moulded to the final base. In the moulding operation the wiringpattern is usually brought to penetrate into the final base. After finalcuring or hardening the temporary base is removed, for instance byetching. This method which has been described in connection withordinary copper layer thicknesses has often the purpose of providing afinal printed circuit in which the surface of the wiring pattern issituated at the same level as the surrounding surface of the insulatingbase. This makes it possible to use so-called glide contacts in thecircuit arrangement for which the circuit is to be used. However, it hasturned out that this known method has certain inconveniences which cancause trouble at least in certain applications. Some of theseinconveniences have been discussed in the British Pat. No. 1 116 299,and in connection with the present invention it shall be further pointedout that practical and economical difficulties arise when the methodshall be used for the production of printed circuits with a very highdegree of precision which is required i.a. in the manufacture ofcircuits with very narrow wiring pattern conductors and very smalldistances between the conductors. After the etching the temporary basewith the wiring must be handled and transported and moulded to the finalinsulating base and these steps combine to decrease the accuracy of themethod. It is also to be understood that the method is practicallyunusable if laminates with wiring patterns on each side of the finalbase and with so-called through-holes plating shall be produced. Finallyit should be pointed out that an increase of the thickness of the copperconductors on the final base is connected with great difficulties if ahigh degree of accuracy is desired.

The inconveniences of the known methods pointed out above are avoided toa very high degree by the application of the present invention.

A method according to the invention for the production of a material forprinted circuits which material comprises a layer of metal on aninsulating base is characterized in that a thin, unbroken andunpatterned metal layer having a thickness less than 17 μm is applied byelectroplating to a temporary base, preferably of a throw-away type, inthe form of a metal foil of aluminum, zinc or their alloys or steel,that the free surface of the said, on the temporary base electroplated,thin metal layer is brought to a strong adhesion to a final, insulatingbase and that the temporary base is removed, whereupon desired wiringpatterns of printed circuits can be produced by a process comprisingetching of the metal layer bound to the final insulatng base.

The thickness of the thin metal layer, should according to the inventionbe between 1 and 15 μm, preferably between 2 and 10 μm, and can be, forinstance about 5 μm.

It is not necessary to carry out the various steps of the methodaccording to the invention one immediately after the other and in oneand the same locality but the procedure can be divided in time and spaceby separately producing one or more intermediate products which arethereafter subjected to complementary treatment for carrying out thecomplete method according to the invention.

The thin metal layer which is to form the wiring pattern can suitablyconsist of copper or nickel or their alloys. The metal layer can be asingle layer or consist of a combination of two or more layers ofdifferent metals or alloys thereof. Other metals than those mentionedabove and other combinations of metals can also be used.

The final, insulating base can suitably consist of a stiff sheet ofplastic which may be fibre-reinforced, for instance of a sheet of glassfibre reinforced epoxy resin, but it can also consist of a plastic filmwhich may likewise be fibre-reinforced.

According to a further development of the invention for applicationespecially in the case when a foil of aluminum or an alloy thereof isused as a temporary base a relatively thin layer of zinc, tine or theiralloys can be applied on the surface of the temporary base facing themetal layer, before applying the metal layer by electroplating.

The invention also relates to a material for printed circuits producedby the method according to the invention and to materials intended to beused in the form of intermediate products for carrying out the methodaccording to the invention. A first intermediate product consists of atemporary base of a throw-away type in the form of a foil of aluminum,zinc or their alloys or steel with at least one unbroken or continuous,thin layer of metal applied by electroplating, said layer having athickness less than 17 μm, suitably a thickness of 1 - 15 μm, andpreferably a thickness of 2 - 10 μm. A second intermediate productconsists of said first intermediate product laminated or moulded withthe final insulating base with the thin metal layer facing the finalbase and bound thereto.

The invention will be more fully described hereinbelow with reference tothe drawings. In the drawings,

Figs. 1 - 3 illustrate the influence of the thickness of the copperlayer on the so called undercut in an etching procedure.

FIGS. 4 - 10 illustrate a method according to one embodiment of theinvention.

FIG. 11 illustrates a modified method.

FIGS. 12 - 14 illustrate a method according to the invention in whichthe thickness of the wiring pattern forming portions of a thin metallayer are increased by plating, whereupon the other portions of themetal layer are removed by etching.

FIG. 15 illustrates the result after a so called through-holes plating.

FIG. 16 shows schematically a device for producing, according to theinvention, materials for printed circuits and

FIG. 17 illustrates schematically a further embodiment of the methodaccording to the invention.

In FIGS. 1 - 3 there is shown in cross-section a metal layer of copper2',2" and 2"' respectively, of a printed circuit, said layer beingbonded to an insulating base 1 and covered by an etch resist 3. In FIG.1 the reference 4 designates the cavity in the metal layer under theetch resist caused by the etching. U' being the measure of the undercut.In FIGS. 2 and 3 the undercut is designated with U" and U'"respectively. The metal layer 2' according to FIG. 1 is relativelythick, about 35 μm, and requires a long etching time, the undercut beingin this case considerable. The metal layer 2" in FIG. 2 is thinner,about 17 μm, and the undercut U" is considerably less than U' in FIG. 1.The metal layer 2'" is very thin, for instance about 5 μm, and requiresonly a short etching time. The undercut U"' is here neglectable even atvery small width of the conductors formed by the metal layer.

FIGS. 4 - 10 illustrate a method according to the invention. On atemporary base 5, FIG. 4, of aluminum a thin copper layer 6, FIG. 5,with a thickness less than 17 μm, is deposited by electroplating. Thematerial according to FIG. 5 is thereafter laminated or moulded with afinal, insulating base 7, for instance of glass fibre reinforced epoxyresin, with the copper layer facing the final base, FIG. 6, whereuponthe temporary base 5 is removed, for instance by peeling or by etching.On the product, FIG. 7, thus obtained an etch resist 8, FIG. 8, is thenapplied, which corresponds to a desired pattern, whereupon the uncoveredportions of the thin copper layer are removed by etching, FIG. 9. Afterdissolving the etch resist 8 the final printed circuit is obtained, FIG.10.

The material shown in FIG. 7 can, as shown in FIGS. 8 and 9, be used assuch, in which case the advantage is obtained that the undercut isneglectable. This advantage can, however, be maintained also if it isdesired to produce wiring patterns with increased conductor thickness,and FIGS. 12 - 14 show how this can be achieved.

On an insulating base 11 a copper layer 12 with a thickness of, forinstance, 5 μm has been deposited by means of a method according to theinvention. For increasing the thickness of the conductors a mask 13corresponding to the negative of the desired conductor pattern is firstapplied to the copper layer 12, as shown in FIG. 12. Thereafter furthercopper 16 is deposited on the layer 12 by electroplating until thedesired conductor thickness, for instance 35 μm, has been obtainedwhereupon a different metal serving as an etch resist 17 is applied tothe deposited copper, all as shown in FIG. 13. Finally the mask 13 isdissolved and the thin copper layer covered by the mask is removed byetching which takes only a short time. The result is shown in FIG. 14from which appears that a conductor with a considerable thickness, forinstance 35 μm, and with very accurate dimensions has been achieved, thelatter thanks to the absence of mentionable undercut.

In FIG. 15 a so called through-holes plating method is illustrated whichcan suitably be carried out simultaneously with plating for achievingincreased conductor thickness are illustrated in FIGS. 12 - 14. Aninsulated base 21 is provided on each side thereof with a very thincopper layer 22a and 22b respectively, by a method according to theinvention. In the composite material through-going holes 24 have beenmade, for instance by drilling. After pretreatment of the holes andafter masking in a known manner plating is carried out whereby thedeposited copper material is applied on the unmasked portions of thethin copper layer and on the inner walls of the holes until the desiredplating thickness has been achieved. After removing the mask and etchingthe underlying portions of the copper layer the final product shown inFIG. 15 is obtained. It appears that the deposited copper layers 23a onthe thin copper layers and the deposited copper layers 23b on the wallsof the holes 24 become approximately equally thick and have goodconnection to each other which is of great importance from the point ofview of reliability.

The temporary base used in the method according to the invention needand should not be thicker than what is required for forming andsupporting the thin copper layer so that the composite materialconsisting of the temporary base and the copper layer can be handledcomfortably during the further processing. The temporary base shouldpreferably be of the throw-away type so that is can be destroyed afteruse. The thickness of the temporary base depends on the stiffness of thematerials used but should suitably be not more than 0.2 mm, preferablynot more than 0.1 mm and can be, for instance, about 0.03 mm. A furtheradvantage with the invention is that the temporary base can serve asprotection against oxidation, scratching and other damage of the thinmetal layer during transport, storing and mechanical treatment of thelaminate. The temporary base is then removed in connection with themanufacture of the printed circuit.

Another advantage is related to the aforementioned presence ofthrough-going holes, so called micropores, in the copper layer, saidmicropores being difficult to avoid in an electroplating process. Thesemicropores create, as mentioned, difficulties, since part of the resinflows up to the surface of the copper through the micropores during thehigh pressure moulding applied for the manufacture of, for instance,glass cloth reinforced epoxy resin laminate. The patches of eopxy resinon the copper surface are highly harmful in the manufacture of theprinted circuit both in the etching, plating and soldering steps. Thethinner the copper foil the more difficult it is to avoid this problem.The present invention solves the problem, since the temporary baseconstitutes an effective barrier during the moulding operationpreventing any flow-up of resin on the surface of the copper layer.

Before the temporary base with an even copper layer is moulded to thefinal base it is suitable to subject the copper to a surface treatmentfor improving the bond between the copper and the resin of the finalbase. This surface treatment often makes the surface of the copperuneven. The thickness of the deposited copper layer is thereforecalculated as an average thickness. An average thickness of 10 μmcorresponds to a surface weight of about 87 g/m².

The method according to the invention is further illustrated by thefollowing examples.

EXAMPLE 1

An aluminum foil (50 μm) was washed in a cleaning solution consisting ofwater, sodium carbonate and sodium phosphate. The foil was then washedin water and was thereafter electroplated in a water solution containing

    ______________________________________                                        Cu(CN).sub.2         25 g/l                                                   NaCN                 20 g/l                                                   Na.sub.2 CO.sub.3    30 g/l                                                   NaOH                  3 g/l                                                   Rochelle salt        70 g/l                                                   ______________________________________                                    

for 2 minutes at 45° C with a current density of 15 mA/cm². Afterwashing the foil was plated for 2 minutes with a current density of 50mA/cm² at a temperature of 42° C in a water bath containing

    ______________________________________                                        CuSO.sub.4           170 g/l                                                  H.sub.2 SO.sub.4      50 g/l                                                  ______________________________________                                    

Thereafter the electroplating was carried out in the same bath at acurrent density of 200 mA/cm² during 2 minutes for achieving a surfacewith high crystallinity and good adhesion to epoxy resin. A copper layerwith a thickness of 5 μm was obtained.

After the plating the aluminum foil was washed and dried whereupon itwas placed on a few sheets of an epoxy resin inpregnated glass web withthe copper coated surface facing said sheets. The laminate was mouldedunder pressure and the aluminum foil could be peeled off after themoulding operation.

The copper layer bound to the final laminate had an adhesion to thebase, a so-called peel strength, of 8.5 lbs/in measured according to thestandardized measuring method ASTM D/1867 after increasing the thicknessof the copper layer by plating to 35 μm. The thickness of the metallayer obtained by plating can be changed in a simple manner by varyingthe plating time and/or the current density. On the laminate thusobtained a wiring pattern for the desired printed circuit was thereafteretched in a manner known per se.

EXAMPLE 2

A laminate was produced in the same manner as according to Example 1 butthe aluminum foil was etched away in hydrochloric acid instead of beingremoved mechanically by tearing. The peel strength was 9.0 lbs/in.

EXAMPLE 3

A zinc foil (80 μm) was plated in a bath consisting of

    ______________________________________                                        CuSO.sub.4 . 5H.sub.2 O                                                                            220 g/l                                                  H.sub.2 SO.sub.4     100 g/l                                                  ______________________________________                                    

during 2 minutes at 20° C with a current density of 100 mA/cm². Afterwashing the foil was plated during 20 seconds at room temperature in thesame plating bath with a current density of 500 mA/cm². Thereafterplating took place in the same bath for 30 seconds at a current densityof 50 mA/cm². A copper layer of 6 μm was thereby obtained. Aftermoulding according to Example 1 the zinc foil was etched away by meansof hydrochloric acid. On the final laminate the copper layer had a peelstrength of 12 lbs/in.

EXAMPLE 4

A steel foil (100 μm) was plated in a bath consisting of

    ______________________________________                                        CuP.sub.2 O.sub.7     50 g/l                                                  K.sub.2 P.sub.2 O.sub.7                                                                            250 g/l                                                  ______________________________________                                    

for 2 minutes at 35° C with a current density of 24 mA/cm². Afterwashing the foil was plated for 3 minutes at 35° C in a plating bathconsisting of

    ______________________________________                                        CuSO.sub.4 . 5H.sub.2 O                                                                            225 g/l                                                  H.sub.2 SO.sub.4     100 g/l                                                  ______________________________________                                    

at a current density of 100 mA/cm².

The foil was thereafter plated at 35° C in the same bath for 20 secondsat a current density of 500 mA/cm². Thereafter the foil was plated onceagain at 35° C in the same bath for 20 seconds at a current density of100 mA/cm².

A copper layer with a thickness of 10 μm was obtained. After moulding asaccording to Example 1 the steel foil could be peeled off. The copperlayer of the final laminate had a peel strength of 10.5 lbs/in.

EXAMPLE 5

An aluminum foil was plated with a 5 μm thick copper layer in the mannerdescribed in Example 1. Thereafter the foil was moulded under heat andpressure to a 75 μm thick plastic film of the type polyethyleneterephthalate with the copper coated surface facing the film. As bindingagent heat curing polyurethane resin was used. After the bonding of themetal foil to the plastic film the aluminum foil could be peeled off. Aflexible laminate consisting of a plastic film coated with a 5 μm thickcopper layer was obtained.

EXAMPLE 6

An aluminum foil was plated with a 10 μm thick copper layer in themanner described in Example 1. Thereafter the foil was placed on a sheetof "non-woven" cloth of polyester fibre which had been impregnated witha partly cured epoxy resin, the copper coated surface of the foil facingthe impregnated cloth. After moulding at a raised temperature thealuminum foil could be peeled off. The copper clad laminate obtained hadgood flexibility.

EXAMPLE 7

An aluminum foil was plated with a 3 μm thick copper layer in the mannerdescribed in Example 1. Thereafter the copper clad surface of the foilwas coated with a 75 μm thick layer of partly cured epoxy resin of theheat resistant type. A 1 mm thick copper plate was also coated with a 75μm thick layer of partly cured epoxy resin of the same type. Byelectrolytical treatment the copper plate had been rendered a surfacegiving good adhesion to epoxy resin. The foil and the copper plate wasmoulded together under heat and pressure with the epoxy resin coatedsurfaces facing each other. Thereafter the aluminum foil was etched awayin hydrochloric acid. The final laminate consisted of a copper plate anda 3 μm thick copper layer with an electrically insulating layer of epoxyresin therebetween. The copper plate assured effective dissipation ofheat from a heated article which was soldered to the thin copper layer.

From an economical point of view the most advantageous temporary base tobe used in the method according to the invention is an aluminum foilwhich is cheap, easy to etch and gives less dangerous waste productsfrom the point of view of environment protection. The use of such a foilis, however, not free from problems. It is difficult to obtain a goodadhesion in the application by plating of a metal layer on an aluminumfoil. This is true i.a. if it is desired to apply a copper layer on thefoil. In this case it is usually necessary to utilize a cyanidecontaining plating bath which gives rise to waste products which aredangerous to the environment. The handling of cyanides during theplating process is also connected with risks.

According to an embodiment of the invention a temporary base of aluminumfoil is used which is coated with a thin layer of zinc or tin,preferably with a thickness less than 2 μm, and the thin metal layer isthen applied to the zinc or tin coating by electroplating. The adhesionbetween the metal, for instance copper, and the zinc or tin layer isvery good, and one can also avoid the use of cyanide containingsolutions, if desired. FIG. 11 shows how a temporary base 5 of aluminumhas been provided with a thin layer of zinc 9 on which a copper coating6 has thereafter been deposited by electroplating.

EXAMPLE 8

A hard-rolled aluminum foil was treated for 1 minute at room temperaturein a zincate solution consisting of

    ______________________________________                                        ZnO                   95 g/l                                                  NaOH                 520 g/l                                                  ______________________________________                                    

After the treatment it was found that the foil was covered by a layer ofzinc. The zinc layer was dissolved by immersion in 50 % HNO₃, whereby aclean aluminum surface was obtained. The aluminum foil was thereaftertreated once again in the above-mentioned zincate solution for 1 minuteat room temperature, whereby a thin zinc layer with good adhesion to thealuminum foil was obtained.

The aluminum foil thus treated was plated with nickel in a Wattssolution consisting of

    ______________________________________                                        Nickel sulphate      300 g/l                                                  Nickel chloride       45 g/l                                                  Boric acid           180 g/l                                                  ______________________________________                                    

for 3 minutes at 50° C and a current density of 50 mA/cm². Thereafterthe plating was continued for 1 minute in the same bath at 50° C andwith a current density of 150 mA/cm².

The plated aluminum foil was placed on a few sheets of epoxy resinimpregnated glass cloth with the nickel coated surface facing saidcloth. The laminate was moulded and the aluminum foil with the zinclayer could be dissolved by means of H₂ SO₄. A laminate coated with a 5μm thick nickel layer was obtained. The strength of the bond between thenickel layer and the epoxy glass fibre laminate, the peel strength,measured on a 35 μm thick foil was 12 lbs/in.

EXAMPLE 9

A hard-rolled aluminum foil was immersed for 3 minutes in a 5%NaOH-solution. Thereafter the foil was immersed for 1 minute in azincate solution of

    ______________________________________                                        NaOH                 60 g/l                                                   ZnO                  6 g/l                                                    FeCl.sub.3 . 6H.sub.2 O                                                                            2 g/l                                                    Rochelle salt        55 g/l                                                   NaNO.sub.3           1 g/l                                                    ______________________________________                                    

The zinc-treated aluminum foil was plated with brass for 6 minutes at60° C and a current density of 40 mA/cm² in a bath containing

    ______________________________________                                        CuCN                 55 g/l                                                   .[.Zn .].(CN).sub.2  31 g/l                                                   NaCN                 95 g/l                                                   Na.sub.2 CO.sub.3    35 g/l                                                   NH.sub.4 OH          10 g/l                                                   ______________________________________                                    

A laminate was produced in the same manner as according to Example 8.The temporary base could be dissolved by means of H₂ SO₄ after themoulding. A laminate with a 4 μm thick brass layer was obtained. Theproportion between copper and zinc of the brass was about 70:30. Thepeel strength was 6 lbs/in.

EXAMPLE 10

A hard-rolled aluminum foil was zinc-treated in the same manner asaccording to Example 8. Thereafter the foil was plated with brass for 5minutes at room temperature and a current density of 50 mA/cm² in a bathcontaining

    ______________________________________                                        CuCN                 20 g/l                                                   Zn(CN).sub.2         45 g/l                                                   NaCN                 50 g/l                                                   Na.sub.2 CO.sub.3    32 g/l                                                   NaOH                 30 g/l                                                   Rochelle salt         5 g/l                                                   ______________________________________                                    

A laminate was produced in the same manner as according to Example 8.The temporary base could be dissolved by means of H₂ SO₄ after themoulding. A laminate with a 5 μm thick layer of brass was obtained. Theproportion between copper and zinc of the brass was about 40:60. Thepeel strength was 6 lbs/in.

EXAMPLE 11

An aluminum foil which had been zinc-treated according to Example 8 wasplated at room temperature for 1, 2, 5 or 10 minutes respectively at acurrent density of 60 mA/cm² in an acid copper solution containing

    ______________________________________                                        CuSO.sub.4 . 5H.sub.2 O                                                                            200 g/l                                                  H.sub.2 SO.sub.4      70 g/l                                                  ______________________________________                                    

Thereafter the foil was plated at room temperature in the same solutionfor 20 seconds at a current density of 200 mA/cm² and thereafter for afurther period of 20 seconds at a current density of 50 mA/cm².

Laminates were produced in the same manner as according to Example 8.After the moulding the temporary base was peeled off. The laminates werecoated with a copper layer with a thickness of 4 μm, 5 μm, 8 μm and 13μm respectively. The adhesion to the final base was about 11 lbs/in.

The thickness of the metal layer obtained by plating can thus simply bechanged by varying the plating time which is shown in Example 11.

FIG. 16 illustrates schematically a continuous process according to theinvention for the manufacture of a material for printed circuitsconsisting of an aluminum foil with a very thin copper coating depositedthereon. An aluminum foil 32 is drawn from a storage roll 31 and isfirst led through a cleaning bath 33 and thereafter through a washingtube 34 containing Na₂ CO₃ Na₃ PO₄ or NaOH whereafter the foil ispretreated by means of a zincate or stannate solution 35 for depositinga thin layer of zinc and tin, respectively, on the aluminum foil. Afterrenewed washing in a suitable liquid 36 the foil is led down into asoluton 37 in a device for electroplating the surface of the foil coatedwith zinc and tin, respectively, for obtaining a thin copper layerthereon. The solution 37 can be, for instance, a solution of coppersulphate, copper pyrophosphate or copper cyanide. The foil on the roll40 serves as a cathode and the plate 41 as an anode at theelectroplating procedure. After the plating the product is washed in abath 43 and is dried by means of a device 38, whereupon the coppercoated aluminum foil 42 thus obtained is wound up on the roll 39. Thedescribed process serves only as an illustration. Certain process stepscan be eliminated and other can be added. Thus, for instance, furtherplating steps can be required in certain cases.

The present invention also relates to a modified method which isespecially advantageous technically and economically in the manufactureof certain types of metal coated plastic films. According to this methodthe thin metal layer carried by the temporary base is coated with alayer of a resin solution or a prepolymer or a solution of a prepolymer.It is also possible to use resin dispersions, melts or other liquidphases of the resin or its prepolymer. The deposited layer istransformed to solid phase for instance by evaporation of the solventand polymerizing the prepolymer. Thereafter the temporary base can beremoved, whereupon a plastic film coated with the very thin metal layeris obtained. Examples of metal coated plastic films which can bemanufactured with advantage by means of this process are films ofpolybenzoxazole, polybenzimidazole, polyimide and polybutadiene resins.These plastics have good dielectric properties and good heat resistancewhich is advantageous in printed circuitry. Such metal coated plasticfilms find use for instance in the manufacture of flexible printedcircuits.

FIG. 17 illustrates schematically a continuous process according to thismodified method. From a storage roll 51 for a foil 52 which, if desired,can consist of the final product 42 obtained by the process according toFIG. 16, the foil is drawn horizontally over a support 53, it beingassumed that the underside of the horizontal foil is constituted by atemporary base in the form of a metal foil 52a and the upper side isconstituted by a metal foil deposited on the temporary base by means ofelectroplating and consisting of a thin layer 52b, for instance ofcopper. From a container 54 for a fluid prepolymer 55 of a resinsuitable for forming a final, insulating base of the material forprinted circuits to be produced the metal layer is coated with theprepolymer which is thereafter brought to final polymerization by meansof a suitable apparatus 57 whereby a strong, flexible film 56 isobtained. After removing the metal foil 52a which is wound up on a roll59 the film 56 with the thin metal coating bonded thereto is wound up ona roll 58. For the sake of simplicity further process steps which can berequired, for instance pretreatment of the component foil materials havenot been shown in FIG. 17. From the roll 59 the metal foil can go toreplating, if desired. Instead of peeling off the temporary base thelatter can be removed in any other manner for instance by etching, whichcan be carried out with advantage in immediate connection with themanufacture of the printed circuit.

EXAMPLE 12

An aluminum foil with a copper layer with a thickness of 5 μm wasproduced according to Example 11. The free copper surface was coatedwith a layer of a solution consisting of

    ______________________________________                                        Polybenzoxazole, prepolymer                                                                        15 parts by weight                                       Dimethylacetamide    85 parts by weight                                       ______________________________________                                    

The dimethylacetamide was evaporated in an oven while graduallyincreasing the temperature from 60° C to 160° C for 60 minutes.Thereafter the temperature was increased to 300° C which temperature wasmaintained for 45 minutes. During the last mentioned treatment which wascarried out in a nitrogen gas atmosphere the prepolymer underwent achemical reaction so that an aromatic polybenzoxazole was obtained.

Thereafter the aluminum foil was etched away by means of hydrochloricacid. As a result a 25 μm thick film of polybenzoxazole plastic coatedwith a 5 μm thick copper layer was obtained. The plastic film proper hadhigh flexibility and a very good heat resistance at temperatures up to250° C. The tensile strength was 1050 kp/cm² at 20° C.

The invention is not limited to the embodiment examples shown anddescribed since they can be modified in different manners within thescope of the invention.

I claim:
 1. A method for the production of a material for printedcircuits by transferring a metal layer via a temporary base to aninsulating, final base, comprising electroplating a continuous layer ofcopper or a copper alloy to a temporary base of a throw-away type, inthe form of a foil of aluminum or alloy thereof having a thickness lessthan 200μm, electroplating copper or a copper alloy for at least onefurther step to form at least one further layer by changing at least oneof the plating variables of current density and composition of theelectroplating bath of the first step to improve the adhesion to thefinal base, said electroplated layers having a combined thickness of1-17 μm measured by weight, placing at least one side of a materialconsisting of partially cured fiber reinforced thermosetting plastictowards such electroplated layers of copper or copper alloy of such atemporary base, laminating under heat and pressure to cure said plasticthereby forming the final base and bringing about an adhesion betweenthe electroplated layers and the final base amounting to at least 6lbs/in and removing the temporary base in connection with the printedcircuit manuacturing by etching, stripping, tearing off or a combinationthereof, leaving the thin, electroplated metal layers on the final base.2. A method according to claim 1 characterized in that the combinedthickness of the thin metal layers is 1-15 μm.
 3. A method according toclaim 1 characterized in that the combined thickness of the thin metallayers is 2-10 μm.
 4. A method according to claim 1 characterized inthat the combined thickness of the thin metal layers is about 5 μm.
 5. Amethod according to claim 1 characterized in that the final, insulatingbase consists of glass fiber reinforced epoxy resin.
 6. A methodaccording to claim 1 characterized in that the surface of the temporarybase facing said thin metal layers is treated, before the electroplatingprocess, for assuring a satisfactory adhesion to the deposited metallayers.
 7. A method according to claim 1 characterized in that thesurface of the temporary base facing said thin metal layers is coated,before the electroplating process, with a layer of zinc, tin or theiralloys.
 8. A method according to claim 1 characterized in that saidtemporary base in the form of a foil of aluminum, or an alloy thereof iscontinuously fed through an apparatus in which said thin, continuouslayers of copper or a copper alloy are deposited by electroplating on atleast one side of the temporary base.
 9. A method for the production ofa material for printed circuits by transferring a metal layer via atemporary base to an insulating fuel base, comprising electroplating acontinuous, even layer of copper or a copper alloy to a temporary baseof a throw-away type, in the form of a foil of aluminum or alloy thereofhaving a thickness less than 200 μm, electroplating copper or a copperalloy for at least one further step to form at least one further layerhaving an uneven surface by changing at least one of the platingvariables of current density and composition of the electroplating bathof the first step to improve the adhesion to the final base, saidelectroplated layers having a combined thickness of 1-17 μm measured byweight, placing at least one side of a material consisting of partiallycured fiber reinforced thermosetting plastic towards such electroplatedlayers of copper or copper alloy of such a tempoarary base, laminatingunder heat and pressure to cure said plastic thereby forming the finalbase and bringing about an adhesion between the electroplated layers andthe final base amounting to at least 6 lbs/in and removing the temporarybase in connection with the printed circuit manufacturing by etching,stripping, tearing off or a combination thereof, leaving the thin,electroplated metal layers on the final base. .Iadd.
 10. A method forthe production of a material for printed circuits comprisingelectroplating a continuous layer of copper or a copper alloy to atemporary base of a throw-away type, in the form of a foil of aluminumor alloy thereof having a thickness less than 200 μ m and electroplatingcopper or a copper alloy for at least one further step to form at leastone further layer by changing at least one of the plating variables ofcurrent density and composition of the electroplating bath of the firststep to improve the adhesion to a final base, said electroplated layershaving a combined thickness of 1-17 μ m measured by weight. .Iaddend..Iadd.
 11. A method according to claim 10 characterized in that thecombined thickness of the thin metal layers is 1-15 μ m. .Iaddend..Iadd.
 12. A method according to claim 10 characterized in that thecombined thickness of the thin metal layers is 2-10 μ m. .Iaddend..Iadd.13. A method according to claim 10 characterized in that thecombined thickness of the thin metal layers is about 5 μ m. .Iaddend..Iadd.14. A method according to claim 10 characterized in that thesurface of the temporary base facing said thin metal layers is treated,before the electroplating process, for assuring a satisfactory adhesionto the deposited metal layers. .Iaddend. .Iadd.15. A method according toclaim 10 characterized in that the surface of the temporary base facingsaid thin metal layers is coated, before the electroplating process,with a layer of zinc, tin or their alloys. .Iaddend. .Iadd.16. A methodaccording to claim 10 characterized in that said temporary base in theform of a foil of aluminum, or an alloy thereof is continuously fedthrough an apparatus in which said thin, continuous layers of copper ora copper alloy are deposited by electroplating on at least one side ofthe temporary base. .Iaddend. .Iadd.17. A method for the production of amaterial for printed circuits comprising electroplating a continuous,even layer of copper or a copper alloy to a temporary base of athrow-away type, in the form of a foil of aluminum or alloy thereofhaving a thickness less than 200 μ m, and electroplating copper or acopper alloy for at least one further step to form at least one furtherlayer having an uneven surface by changing at least one of the platingvariables of current density and composition of the electroplating bathof the first step to improve the adhesion to a final base, saidelectroplated layers having a combined thickness of 1-17 μ m measured byweight. .Iaddend. .Iadd.18. A method for the production of a materialfor printed circuits by transferring a metal layer via a temporary baseto an insulating, final base, comprising electroplating a continuouslayer of copper or a copper alloy to a temporary base of a throw-awaytype, in the form of a foil of aluminum or alloy thereof having athickness less than 200 μ m, electroplating copper or a copper alloy forat least one further step to form at least one further layer by changingat least one of the plating variables of current density and compositionof the electroplating bath of the first step to improve the adhesion tothe final base, said electroplated layers having a combined thickness of1-17 μ m measured by weight, placed at least one side of a materialconsisting of partially cured fiber reinforced thermosetting plastictowards such electroplated layers of copper or copper alloy of such atemporary base and laminating under heat and pressure to cure saidplastic thereby forming the final base and bringing about an adhesionbetween the electroplated layers and the final base amounting to atleast 6 lbs/in. .Iaddend..Iadd.19. A method according to claim 18chacterized in that the combined thickness of the thin metal layers is1-15 μ m. .Iaddend. .Iadd.20. A method according to claim 18characterized in that the combined thickness of the thin metal layers is2-10 μ m. .Iaddend. .Iadd.21. A method according to claim 18characterized in that the combined thickness of the thin metal layers isabout 5 μ m. .Iaddend. .Iadd.22. A method according to claim 18characterized in that the final, insulating base consists of glass fiberreinforced epoxy resin. .Iaddend. .Iadd.23. A method according to claim18 characterized in that the surface of the temporary base facing saidthin metal layers is treated, before the electroplating process, forassuring a satisfactory adhesion to the deposited metal layers..Iaddend. .Iadd.24. A method according to claim 18 characterized in thatthe surface of the temporary base facing said thin metal layers iscoated, before the electroplating process, with a layer of zinc, tin ortheir alloys. .Iaddend. .Iadd.25. A method according to claim 18characterized in that said temporary base in the form of a foil ofaluminum, or an alloy thereof is continuously fed through an apparatusin which said thin, continuous layers of copper or a copper alloy aredeposited by electroplating on at least one side of the temporary base..Iaddend. .Iadd.26. A method for the production of a material forprinted circuits by transferring a metal layer via a temporary base toan insulating, final base, comprising electroplatinc a continuous, evenlayer of copper or a copper alloy to a temporary base of a throw-awaytype, in the form of a foil of aluminum or alloy thereof having athickness less than 200 μ m, electroplating copper or a copper alloy forat least one further step to form at least one further layer having anuneven surface by changing at least one of the plating variables ofcurrent density and composition of the electroplating bath of the firststep to improve the adhesion to the final base, said electroplatedlayers having a combined thickness of 1-17 μ m measured by weight,placing at least one side of a material consisting of partially curedfiber reinforced thermosetting plastic towards such electroplated layersof copper or copper alloy of such a temporary base and laminating underheat and pressure to cure said plastic thereby forming the final baseand bringing about an adhesion between the electroplated layers and thefinal base amounting to at least 6 lbs/in. .Iaddend. .Iadd.27. Themethod of bonding a laminate, said laminate being made up of a layer ofaluminum or allow thereof and at least two layers of copper, to a layerof partially cured fiber-reinforced thermosetting plastic, said laminatehaving been obtained by electroplating a continuous layer of copper or acopper alloy to a layer in the form of a foil of aluminum or alloythereof having a thickness of less than 200 μ m, electroplating copperor a copper alloy for at least one further step to form at least onefurther by changing at least one of the plating variables of currentdensity and composition of the electroplating bath of the first step,said electroplated layers having a combined thickness of 1-17 μ mmeasured by weight, this method comprising placing at least one side ofsaid layer of partially cured fiber-reinforced thermosetting plastictowards such electroplated layers of copper or copper alloy, laminatingunder heat and pressure to cure said plastic and bringing about anadhesion between the electroplated layers and the said plastic amountingto at least 6 lbs/in. .Iaddend.